Nuclear export of messenger RNAs (mRNAs) and their subsequent translation are essential steps in the gene expression pathway and impact all aspects of cell physiology. There is a growing body of evidence suggesting that dysfunctional mRNA trafficking contributes directly to motor neuron diseases (MND). This is further supported by the recent genetic linkage of mutant human GLE1 alleles to the fetal motor neuron disease: Lethal Congenital Contracture Syndrome (LCCS-1). Gle1 is an essential mRNA export factor, conserved from yeast to humans. Yeast Gle1 plays an important role in both translation initiation and termination. Sequence analysis of genomic DNA from LCCS-1 cases identified a mutation that generates an illegitimate splice acceptor site within the third intron of GLE1. This specific mutation (FINMajor) results in an insertion of three amino acid residues (PFQ) in the amino-terminal domain of hGle1. In preliminary studies a novel function for hGle1 in cytoplasmic mRNA trafficking has been found. Strikingly, the FINMajor mutation may disrupt hGle1's function in trafficking. The goal of this proposal is to elucidate the functional consequence of the FINMajor mutant protein in mammalian cells. The two aims proposed will define the molecular consequence of the FINMajor mutation. In Aim I, studies will be done to define hGle1 as a component of the cytoplasmic mRNA trafficking machinery. In Aim II, a novel hGle1 knockdown, and add-back model system will be developed. With this experimental model, cell biology and biochemical assays will be used to investigate if the FINMajor mutant protein disrupts mRNA trafficking. The long-term goal is to molecularly define the neuronal role for hGle1 in the pathogenesis of the deleterious disease LCCS-1